1. Field of the Invention
This invention relates to an audio signal reproducing apparatus and more particularly to an apparatus arranged to reproduce audio signals from a recording medium having mark signals recorded along with the audio signals to show respectively the positions of the audio signal on the medium.
2. Description of the Prior Art
Heretofore, the audio signal recording and/or reproducing apparatuses have been arranged to perform various additional functions of identification. These functions include a head (or leader part) searching function which is considered indispensable particularly to the recording apparatus of the type arranged to permit long time recording and audio signal recording with a high degree of tone quality.
In accordance with the method conventionally employed for performing the head search function in an audio tape recorder, the tape is allowed to travel at a speed several to several tens of times as fast as the travelling speed employed in recording and then a mute or silent part of the signal thus reproduced with no sound is detected.
Meanwhile, as a result of the recent tendency of having audio signals of high sound quality, there have been proposed various audio signal recording methods of using rotary heads. For example, to obtain an audio signal with high fidelity in a video tape recorder, the audio signal is recorded with frequency modulation by a rotary head. In the case of a tape recorder adapted exclusively for audio signals, it is known to record an audio signal with digital modulation by a rotary head. Further, some known audio recorders are arranged to perform digital modulation recording by time-base compressing an audio signal.
Briefly described, an example of the conventional audio tape recorders of the kind performing digital modulation recording by time-base compressing an audio signal is arranged as follows: FIG. 1 of the accompaying drawings shows by way of example the tape transport system employed in the audio tape recorder of the abovestated kind. The illustration includes a magnetic tape 1; a rotary cylinder 2 which carries a pair of rotary heads 3 and 4. The heads 3 and 4 are thus arranged to obliquely trace the surface of the tape 1 in recording an audio signal on the tape. An audio signal tape recorder capable of exclusively recording audio signals in a total of six channels can be obtained by arranging it to record a time-base compressed audio signal in each of six areas formed on the tape 1 in the longitudinal direction thereof every time these heads 3 and 4 rotate 36 degrees.
The following briefly describes this tape recorder:
FIG. 1 shows the tape transport system of the above-stated tape recorder. FIG. 2 shows recording tracks formed on a tape by this tape recorder. While the head 3 or 4 traces distances from a point A to a point B, from the point B to a point C, from the point C to a point D, from the point D to a point E, from the point E to a point F and from the point F to another point G, audio signals can be recorded in areas CH1 to CH6. These areas CH1 to CH6 thus can be used for recording different audio signals therein respectively. An operation called azimuthoverwrite is performed on these areas. However, the tracks of these areas CH1-CH6 do not have to be on the same straight line. Each of the areas CH1-CH6 has one pilot signal recorded therein for tracking control. Different pilot signals are thus recorded in different areas in the order of rotation fl.fwdarw.f2.fwdarw.f3.fwdarw.f4. However, there is no correlation between them.
Referring further to FIG. 1, recording or reproduction is carried out in or from these areas CH1 to CH3 while the tape 1 is travelling at a predetermined speed in the direction of arrow 7 and in or from the areas CH4 to CH6 while the tape is travelling in the direction of arrow 9. Therefore, as shown in FIG. 2, the inclination of the areas CH1 to CH3 somewhat differs from that of the areas CH4 to CH6. With regard to a difference in the relative speed of the tape and the head for these groups of areas, a difference arising from the travel of the tape 1 is extremely small as compared with a difference arising from the rotation of the heads 3 and 4. Therefore, the difference in the relative speed presents no problem.
FIGS. 3(a) to 3(j) show in a time chart the recording or reproducing operation of the tape recorder which is arranged as described above. A phase detection pulse (hereinafter referred to as a PG signal) which is generated in synchronism with the rotation of the cylinder 2 as shown at FIG. 3(a). The PG signal is of a rectangular wave of 30 Hz repeating a high level (hereinafter referred to as an H level) and a low level (hereinafter referred to as an L level) alternately with each other at intervals of 1/60 sec. Another PG signal which is of the opposite polarity to the PG signal of FIG. 3(a) is shown in FIG. 3(b). The first PG signal is at an H level while the head 3 is rotating from the point B to the point G of FIG. 1. The other PG signal shown in FIG. 3(b) is at an H level while the other head 4 is rotating from the point B to the point G.
Pulses for reading data are obtained from the PG signal of FIG. 3(a) as shown in FIG. 3(c). The data reading pulses are used for sampling the audio signal of a period corresponding to one field (1/60 sec). FIG. 3(d) shows by H level parts thereof periods provided for signal processing on the one field portion of the sampled audio data by adding an error correcting redundant code or by changing the arrangement thereof by means of a RAM or the like. FIG. 3(e) shows a signal indicating data recording periods at H level parts thereof which represent timing for recording, on the tape 1, the recording data obtained through the signal processing operation mentioned above.
Referring to FIGS. 3(a) to 3(j), the temporal flow of signals are, for example, as follows: The data sampled during a period from a point of time t1 to a point of time t3, i.e. while the head 3 is moving from the point B to the point G, is subjected to a signal processing operation during a period from the point of time t3 to a point of time t5, i.e. while the head 3 is moving from the point G to the point A and are then recorded during a period from the point of time t5 to a point of time t6, or while the head 3 is moving from the point A to the point B. In other words, the data is recorded by the head 3 in the area CH1 as shown in FIG. 2. Meanwhile, the data which is sampled while the PG signal of FIG. 3(b) is at an H level is also processed at a similar timing before it is recorded in the area CH1 by the head 4.
FIG. 3(f) shows another PG signal which is obtained by shifting the phase of the PG signal of FIG. 3(a) to a predetermined degree, which corresponds to one area and is 36 degrees in this specific instance.
An audio signal recording operation using the PG signal of FIG. 3(f) and PG signal which is not shown but is of an opposite polarity to the former is performed in the following manner: The data which is sampled during a period between the points of time t2 and t4 is subjected to a signal processing operation during a period between the points of time t4 and t6 in accordance with the signal of FIG. 3(g) and is recorded during a period between the points of time t6 and t7 in accordance with the signal of FIG. 3(h). In other words, the data is recorded in the area CH2 of FIG. 2 while the head is moving from the point B to the point C. Meanwhile, another data which is sampled during the points of time t4 and t7 is likewise recorded in the area CH2 by means of the other head during a period between the points of time t4 and t7.
The signal which is recorded in the area CH2 in the manner as described above is reproduced in the following manner:
The head 3 reads the data from the tape 1 in accordance with a signal shown in FIG. 3(h) during the period between the points of time t6 and t7 (and also during the period between the points of time t1 and t2). Then, during the period between the points of time t7 and t8 also (between t2 and t3), the reproduced signal is subjected to a signal processing operation which is carried out, in a manner reverse to the signal processing operation performed for recording, in accordance with a signal shown in FIG. 3(i). In other words, error correction and other processes are carried out during this period. Then, during a period between points of time t8 and t9, the reproduced audio signal which has been thus processed is produced in accordance with a signal shown in FIG. 3(j). The reproducing operation of the head 4 is of course performed with a phse difference of 180 degrees from the above-stated reproduction by the head 3, so that a continuous reproduced audio signal can be obtained.
For other areas CH3 to CH6, it goes without saying that the recording and reproducing operations are performed on the basis of the PG signal of FIG. 3(a) by phase shifting it as much as n.times.36 degrees. This is independent of the travelling direction of the tape.
It has thus become possible to utilize a VTR specially as a recorder capable of audio signal recording over a long period of time in multiple channel arrangement.
An audio tape recorder of this kind can be readily arranged, for example, to be capable of recording for 90 minutes in each of these channels. Then, the head search function becomes more important. However, there arises the following problem in cases where the direction (hereinafter referred to as "+" or "-" direction) in which the tape is allowed to travel for recording is unknown:
Assuming that some signal is recorded during recording together with an audio signal either between two programs or at a desired part designated by the operator for the purpose of leader search control (hereinafter referred to as an interlude signal), in searching out looking up a leader by detecting the interlude signal, the tape is generally allowed to travel at a high speed for shortening the period of time required for the search. In the case of such a search, the apparatus is preferably arranged to permit designation, before the search, of a desired program, such as designating a search for an audio signal of (+n) after an "n" program or a search for an audio signal of (-m) before an "m" program. However, making such designation is impossible if the "+" or "-" direction in which the tape has travelled for recording is unknown, because: It is impossible to decide in which of the two directions the tape should be moved at a high speed after the designation of "+n" or "-m".
Further, the apparatus is generally arranged to be automatically shifted to the reproduction mode after the search. However, in the above-stated instance, it is impossible to decide in which of the two directions the tape is to be allowed to travel, the "+" direction or "-" direction?.
In a conceivable solution of this problem, some data indicative of the "+" and "-" tape travel directions are arranged to be recorded during a recording operation in addition to the audio signal and pilot signals for tracking control (hereinafter referred to as TPS). This solution, however, necessitates arrangement to record the data in such a format that permits adequate reproduction at a high tape travel speed. Then, the latitude allowable to the recording format for the audio signal would be greatly restricted by such arrangement. This solution is, therefore, not desirable.
In another conceivable solution, either the tape is brought to a stop or the apparatus is shifted to the reproduction mode upon detection of the interlude signal. However, such mode shifting cannot be effected at the recorded position of the interlude signal due to the inertia. Therefore, in the event of a high density record, a portion of the desired program immediately following the leader thereof would be omitted from reproduction with the tape moved at a high speed in the same direction as the recording tape moving direction; or a portion immediately before the end of another program recorded before the desired one would come to be reproduced with the tape moved at the high speed in the direction reverse to the recording direction.